An engine, or power train, e.g. engine and transmission, is usually mounted into the front structure of a motor vehicle. In normal use, the front structure should be strong to resist large loads from engine movements and stiff so as to benefit ride and handling of the vehicle.
As shown schematically in FIG. 1, a suspension for a front, transversely mounted, motor vehicle power plant 1 may be arranged in an automotive frame structure 2 between two front side rails 2a, 2b. The motor vehicle power plant or powertrain refers to a block or unit comprising the engine and/or gearbox of the vehicle 5, but may also comprise further components of the vehicle drive train.
A respective resilient engine mount 4a, 4b is arranged at each side rail 2a, 2b. The engine mounts 4a, 4b are arranged to receive a respective bracket arm 3a, 3b protruding from said motor vehicle power plant 1. The bracket arms 3a, 3b are typically received within a hydraulic unit or a rubber lined cavity arranged within a metal cup or housing. The engine mounts 4a, 4b are arranged to limit motor vehicle power plant 1 movement in a longitudinal direction of the vehicle, i.e. an X-direction, in a lateral direction of the vehicle, i.e. a Y-direction, and in a vertical direction, i.e. a Z-direction (not depicted).
FIG. 2 shows a previously-proposed mounting bracket 10, for attachment to one of the side rails 2a, 2b. The mounting bracket 10 comprises first and second side walls 12a, 12b between which there is a cavity 14 for receiving a resilient member and a bracket arm 3a, 3b (not shown in FIG. 2). Flanges 16a, 16b are provided at the bottom of the side walls 12a, 12b for coupling the mounting bracket 10 to a top surface 18 of the side rail 2a, 2b. Fasteners 20a, 20b in the form of bolts or studs may pass through the flanges 16a, 16b to fasten the mounting bracket to the side rail 2a, 2b. Support structures 22a, 22b may be provided beneath the side rail top surface 18 to provide a bore for the fastener to engage and/or to provide reinforcement to the side rail.
In a motor vehicle crash, the front structure and particularly the front side rails of the motor vehicle should collapse and crumple in a controlled manner to absorb the energy of the crash. In order for the crash energy to be absorbed without intrusion to the passenger compartment, the strength of the car needs to be progressive, i.e. the front structure needs to be weaker than the passenger compartment. A conflict therefore is that the front structure needs to be strong in everyday use but weaker in a crash, and this is particularly true of the engine mounting area.
The arrangement depicted in FIG. 2 adds stiffness to the side rails 2a, 2b. In particular, the mounting bracket 10 structurally reinforces the side rail 2a, 2b over the length of the side rail portion to which the mounting bracket is attached. Such reinforcement may be undesirable as it may affect the crumple performance of the side rail.